Hitherto, many diacylperoxides have been synthesized and studied, and various diacylperoxides useful as initiators in the polymer industries are prepared and commercially available.
The peroxide to be used as a polymerization initiator for a fluorine-containing monomer is generally required to have following characteristics:
1. The fluorine-containing monomer usually has high reactivity, and thus it is desirable to carry out polymerization under milder conditions, for example, at a low temperature. Accordingly, the peroxide is required to liberate an active radical at a low temperature.
2. Since the radicals of the propagating fluorine-containing polymeric chains generated during polymerization are active, side reactions such as chain transfer reactions, do not proceed due to the peroxide.
3. Peroxide residues bonded to the chain ends of the polymer molecules should be thermally stable.
As the peroxides which satisfy the above requirements, there are fluorine-containing diacylperoxides such as EQU [Cl(CF.sub.2 CFCl).sub.n CF.sub.2 COO--.sub.2 (DLP) EQU [H(CF.sub.2 CF.sub.2).sub.n COO--.sub.2 (DHP) EQU [ClCF.sub.2 CF.sub.2 COO--.sub.2 (DIP) EQU [CF.sub.3 CF.sub.2 COO--.sub.2 (3P).
However, these conventional fluorine-containing diacylperoxides are used at a polymerization temperature of 10.degree. to 40.degree. C. or higher to achieve a practical decomposition rate of the peroxide.